An Explanation of the Selective Plating of Laser Machined Surfaces Using Surface Tension Components

LISA (laser induced selective activation) is a new technique for the selective metallization onto polymers for 3D moulded interconnecting devices (3D-MIDs). An Nd:YAG laser was employed to draw patterns on polymer surfaces while the parts were submerged in a liquid (usually water). After subsequent activation with palladium chloride (PdCl(2)) and tin chloride (SnCl(2)) mixtures, followed by auto-catalytic electroless plating, only copper deposited on the laser tracks. The mechanism of the palladium attachment during the activation step was analyzed, based on experimental results and theoretical calculations. It is believed that the porous surface formed after laser machining is the key factor involved in the palladium attachment. The wetting properties of the laser machined surface were studied based on contact angle measurements on both the laser machined and the un-machined surface. Firstly, the hydrophobic characteristics were compared, and it was shown that the surface becomes more hydrophobic after laser machining. Secondly, the polar and apolar components of the surface tension were calculated, according to the acid-base theory by van Oss et al. It was shown that the laser treated surface had a stronger attraction to the activation solution than the surface without the laser treatment. (C) Koninklijke Brill NV, Leiden, 2011